Calling evidence a third party is liable for crime and nexus required

R. v. Murphy, 2012 ONCA 573 deals with calling evidence in a criminal defence that someone other than the accused is the guilty party. In order for such evidence to be admitted there must be some nexus tying the third party to to offence.  However, where the third party is expected to admit guilt and so show the accused innocent that nexus is established:

[19]       Within this framework, the defence has always been permitted to call or adduce evidence that some other person committed the crime with which the accused has been charged.  However, before this third party or alternate suspect evidence can be admitted, the accused bears the burden of showing that the proposed evidence has "some nexus with the alleged offence".  Without the nexus, the evidence would lack probative value.  In R. v. McMillan, (1975), 7 O.R. (2d) 750 (C.A.), at p. 758, Martin J.A. explained the test for the admission for the alternate or third party suspect evidence and its rationale: 

It follows that evidence of the disposition of a third person to commit the crime in question, like other circumstantial evidence, is admissible, if relevant, to prove that the crime was committed by the third person.

Where the character is that of a third person, not a party to the cause, the reasons of policy (noted ante, subsection 64) for exclusion seem to disappear or become inconsiderable; hence, if there is any relevancy in the fact of character, i.e. if some act is involved upon the probability of which a moral trait can throw light, the character may well be received. (Wigmore at p. 488.)

Obviously, unless the third person is connected with the crime under consideration by other circumstances, evidence of such person's disposition to commit the offence is inadmissible on the ground of lack of probative value.  For example, if A is charged with murdering X, in the absence of some nexus with the alleged offence, evidence that B has a propensity or disposition for violence, by itself, is inadmissible to prove B is the murderer because standing alone it has no probative value with respect to the probability of B having committed the offence.  If, however, it is proved that A, B and X all lived in the same house when X was killed, and that B had a motive to kill X, then evidence that B had a propensity for violence may have probative value on the issue whether B, and not A, killed X, and is accordingly admissible.

The Supreme Court of Canada affirmed this test in R. v. Grandinetti, 2005 SCC 5, at paras. 46-48.

[20]       This is the test the trial judge applied in dismissing Murphy's application to call MacLellan as a witness.  The trial judge held that Murphy had not made out a sufficient nexus between MacLellan's proposed evidence and the offences.  In so holding, he misapplied the test in McMillan.

[21]       Both McMillan and Grandinetti deal with the defence's ability to call circumstantial evidence pointing to another person's culpability for the crime – be it evidence of propensity or motive or opportunity.  Without the sort of connections the trial judge found to be absent, this kind of circumstantial evidence would likely not have any probative value. 

[22]       However, Murphy was not seeking to call circumstantial evidence pointing to another suspect.  He was seeking the right to call direct evidence from another person, who was expected to take responsibility for these crimes.  Why, I ask rhetorically, should he not have been permitted to call MacLellan to say, "It is I, not Murphy, who owns the gun and the narcotics the police seized"?  Obviously, it would be for the jury to decide whether to accept that evidence or whether it at least raised a reasonable doubt about Murphy's guilt.  On its face, however, the proposed evidence was sufficiently probative and relevant that the defence should not have been precluded from calling it.